The invention relates to a semiconductor device and, more particularly, to a method for fabricating a photomask.
A pattern including a light blocking layer or a phase shift layer on a substrate is transferred onto a wafer using a photomask as a mask to form a desired pattern on the wafer. In the past, a binary mask has generally been used as the photomask. In the binary mask, the desired pattern is formed as the light blocking pattern on the substrate, and transmitted light passes through the substrate to transfer the desired pattern onto a wafer. However, as the degree of integration of semiconductor devices increases, a wafer that can form a finer pattern than the binary mask on the wafer is required. A phase shift mask that can form a finer pattern on the wafer using a phase shift material having a transmittance of several percent has found widespread use as the photomask.
FIG. 1 illustrates a cross-sectional view of a conventional phase shift mask. Referring to FIG. 1, a phase shift mask includes a phase shift pattern 105 and a light blocking pattern 110 on a transparent substrate 100. A region in which the phase shift pattern 105 is exposed is defined as a phase shift region 115 which shifts the phase of light irradiated onto the substrate 100 during the following exposure process. A region in which the light blocking pattern is exposed is defined as a light blocking region 120 in which the light irradiated onto the substrate 100 is blocked. A region in which the transparent substrate is exposed is defined as a light transmitting region 125 through which the light is passes. The phase shift mask is formed by performing two or more lithography processes using an electron beam (E-beam) exposure unit. There is a limitation that a fine pattern is formed using an E-beam exposure unit because the degree of integration of semiconductor devices increases rapidly. Particularly, a second exposure process using the E-beam exposure unit requires an exposure unit configured to form a finer pattern because accurate pattern alignment is needed. In a laser exposure unit which can form a finer pattern than the E-beam exposure unit, a fabrication process becomes complicated because the laser exposure unit is not adapted to perform a first exposure process. Therefore, there is a need for a method that can form a very fine pattern while simplifying the fabrication process.